1. Field of the Invention
The present invention relates generally to the art of spring motors useful for a variety of applications, including venetian blinds and window shades. More specifically the present invention relates to a system in which lifting cords and cord mechanisms are eliminated from shades or blinds. More specifically the invention relates to window covering systems which, inter alia, employ one or more spring motors to balance the weight of the accumulated window covering material, independent of the extent to which the blind or shade is raised or lowered. Even more specifically, the present invention utilizes an adjustable friction member for engagement with one of a coupled drive and drive actuator to permit the use of spring motors not requiring such rigid specifications.
2. Description of the Art
Venetian blinds have been known for many years and typically include a plurality of slats made from a variety of materials, such as metal, wood, plastic or other materials and supported by ladders.
Such blinds typically include a bottom rail or bar and some kind of tilt mechanism to enable the slats to move from a horizontal position to a nearly vertical position to open and close the blinds with respect to the passage of light. As is also conventional with such systems, flexible line members or lifting cords are coupled to the bottom rail, passing through the slats and into mechanisms within an upper headrail. The cords are employed to raise the bottom rail, accumulating individual slats as the bottom rail is raised. Because of gravity, the natural tendency of the bottom rail and accumulated slat weight is to free fall. In many instances in the prior art, locking mechanisms are employed to lock the bottom rail, and the slats stacked thereon at a height determined by the user. Pleated and other types of shades also include a bottom rail and include similar raising, lowering and line member or cord locking mechanisms.
Spring motors have operating characteristics which find particular utility in conjunction with assisting the elevating and lowering of a variable load such as that provided by venetian blind type window covering. Spring motors are well known in the art and conventionally comprise a flat ribbon of spring metal which is pre-stressed and coiled so as to have a natural or relaxed state in which the spring forms a tightly wound coil disposed on or in a spring storage or take up drum. The extended free end of the coil is attached to the hub of an output or spring drive drum onto which the spring is backwound by rotating the output drum in a direction to back or reverse wind the spring thereon. When the load to which the output drum is connected is released, the curling property of the spring causes it to rewind onto or into the storage drum toward its natural or relaxed state. Such spring motors as described above can be of constant or variable force, depending upon the intended use of the motor. The characteristics of a variable force spring motor can be obtained in varying ways, but varying the radius of curvature of the spring member along the length thereof is conventionally the preferred method.
In connection with the use of such a spring motor and a venetian blind, as an example, a control drum or spool is mounted co-axially with the output drum for rotation therewith, and the flexible member or cord is wound onto the spool in a direction which provides for the unwinding of the cord to rotate the spring output drum in the direction for winding the spring member thereon from the spring storage drum. When the force necessary for such unwinding is relaxed, the spring member returns to its naturally coiled position whereby the spring output drum is rotated by the spring member in a direction to rewind the cord or belt onto the spool. In those blinds with locking mechanism, such rewinding of the cord onto the control drum is inhibited.
When raising or lowering a load such as the bottom rail and slats of a venetian blind, a pair of cords may be wound on the spool in opposite directions with the free ends of the cords attached adjacent the opposite ends of the bottom rail. Such a system is shown in U.S. Pat. No. 5,531,257 issued on Jul. 2, 1996 to Newell Operating Company of Freeport, Ill. When the bottom rail is lowered, the two cords unwind from the spool thus driving the spring output drum to wind the spring member thereon. Upward displacement of the bottom rail from a lowered position results in the spring member rewinding on the spring storage drum to rotate the spring output drum and thus the control drum in the direction to rewind the two cords. In elevating and lowering a suspended load of the foregoing example type, which is too heavy to provide desire displacement characteristics in connection with the upward and downward movement of the bottom rail, and using a single spring motor, many times it is necessary to provide a larger spring motor or operate two or more spring motors in tandem.
When it is desired, the spring motor may be designed to allow the balancing of the gravitational pull on the bottom rail and accumulated slats and the resisting force of the spring motor so that the weight, even though increasing, as additional slats are accumulated on the bottom rail as it is raised, the bottom rail may be released and stay at a predetermined height. However, this is difficult under all conditions.
Because of the differences in materials of the slats, the size of the blind, the number of slats in the blind, the weight of these parts plus the weight of the bottom rail, etc. motors must have different characteristics and be designed for different loads. It is difficult, if not impossible, to utilize the same motors on different types of the slatted blinds as well as shades or fabric covered blinds. The answer of course, heretofore, has been blinds with lifting locks for the cords, or various other means of providing for a balanced blind system. In some, for example U.S. Pat. No. 5,531,257, issued on Jul. 2, 1996 to Newell Operating Company, Freeport Ill., utilize an electric motor to assist and to aid or facilitate the raising and lowering operations.
The motor of a type found in European Patent Application EP 0 796 994 A2 published on Sep. 24, 1997, is illustrative of a spring motor typically employed in a venetian blind system. Each of such motors are of necessity designed with different specifications to account for different loads due to different sizes, materials of the slats, and so forth.